This invention relates generally to a radio broadcast receiver, and more particularly is directed to an improved scanning monitor receiver for scanning a plurality of preselected broadcast channels.
Radio braodcast receivers for monitoring a plurality of preselected broadcast channels are presently in wide use. These radio receivers are customarily used to monitor public safety two-way radio communication channels in one or more of the following three different bands of frequencies assigned by the Federal Communications Commission: the low VHF band from 30 to 50 MHZ; the high VHF bands from 150 to 174 MHZ; and the UHF band from 450 to 520 MHZ. Both public and private agencies, such as police, ambulance, fire, lifeguard, Red Cross and Forest Service are assigned specific frequencies within these bands.
Monitor scanning receivers presently in use customarily provide automatic scanners for selectively tuning the receiver to the preselected channels. For example, individual tuning circuits might be provided for each preselected broadcast channel. These tuning circuits then are sequentially scanned by the automatic scanner. If one of the preselected broadcast channels is active, that is, a radio signal is received, the automatic scanner stops the sequential scanning process and locks onto the active preselected channel. The automatic scanner remains locked on this active channel for the length of the transmission, even though one or more of the other preselected broadcast channels might subsequently become active. At the end of the transmission, the automatic scanner recommences the scanning process and searches for other active preselected channels.
The scanning monitor receivers of the prior art typically are respesented by U.S. Pat. No. 2,739,232 issued to Schwartz on Mar. 20, 1956, U.S. Pat. No. 2,832,889 issued to Kearney on Apr. 29, 1958, and U.S. Pat. No. 2,825,804 issued to Rug on Mar. 4, 1958. These patents show radio receivers which scan a plurality of favorite stations in order to determine whether a radio signal of sufficient strength is present on any one of the favorite stations. If a radio signal of sufficient strength is present, the scanning process is stopped at the appropriate favorite station. While these patents show different methods of station selection, Rug shows a method for scanning only the favorite stations by sequentially scanning a plurality of tuned circuits. However, none of these prior art radio receivers provide the user with the convenient capability of varying the scanning program, that is, the capability of either selecting one or more of the designated favorite stations for scanning or bypassing one or more of the designated favorite stations during scanning.
Some of the radio receivers in the prior art provide the user with the capability of varying the scanning program. For example, U.S. Pat. No. 3,470,481 issued to Meyers on Sept. 30, 1969, shows a scanning monitor receiver for two preselected broadcast channels which also contains an override switch for stopping the sequential scanning process on the selected channel. However, this override switch provides the user with a very limited capability of varying the scanning program.
A much more refined and complicated system for varying the scanning program for a plurality of radio broadcast channels is shown in U.S. Pat. No. 3,845,394 issued to Hamada on Oct. 29, 1974. Hamada discloses an elaborate signal-seeking FM receiver having a pair of memory banks, one of which stores the frequency of all stations receivable in the immediate area, and a second which may be used to store just those stations of immediate interest. Stations for the first memory are determined by scanning the entire radio broadcast band to determine those radio stations with a sufficiently strong radio signal. To select stations for the second memory, stations from the first memory are transferred into the second memory and those which are not desired in the second memory are then removed. Additional stations may also be added to the second memory by means of a relatively complex method. Thus, the second memory embodiment of Hamada does show a method for selecting a subgroup of one or more channels from a larger group of preselected channels. This subgroup may be scanned in the repeat mode by enabling the listener to monitor the contents of the programs broadcast by the several stations. However, this scanning process does not automatically stop on active broadcast channels. The only method of channel selection is manual activation of one of numerous switches provided for this purpose. In addition, Hamada does not show a convenient and simple method for bypassing certain broadcast channels contained in either memory during the scanning process. Therefore, although Hamada does show a fairly comprehensive programming technique for an automatic scanner, the user is unable to easily and instantly reprogram.
Channel selecting devices for televisions also employ mechanisms for bypassing unused television channels and/or preselecting television channels for automatic scanning. For example, U.S. Pat. No. 3,839,681 issued to Mogi on Oct. 1, 1974, shows a system for automatically skipping unused channels and/or preselecting channels to be automatically scanned. Similarly, U.S. Pat. No. 3,602,822 issued to Evans on Aug. 31, 1971, shows a television programmer with an automatic scanning feature for scanning a preselected number of television channels. However, these television scanning systems do not show an automatic scanner which stops scanning in response to the the presence of a signal in the preselected channels. The stopping feature of these television scanners is controlled by the selected program rather than by the presence of a television signal in any preselected television channel. Thus, not only do the above patents not show a combination of a bypass and select mode, but they also fail to disclose an automatic scanner capable of skipping a preselected channel in the absence of an incoming television signal.
It is therefore, an object of this invention to provide a scanning monitor receiver with a scanning selector switch which enables the user to more conveniently control the operation of each preselected broadcast channel. More specifically, it is an object of this invention to enable the user to select one of three possible modes of operation for each preselected broadcast channel: (1) a select mode for scanning a subgroup of one or more preselected channels which does not require the user to set the undesired channels to the bypass mode in order to automatically scan only the desired preselected channels; (2) a scan mode for automatically scanning all preselected broadcast channels; and (3) a bypass mode for bypassing certain preselected broadcast channels to eliminate reception on these bypassed channels.
It is a further object of this invention to provide a selector switch for a scanning monitor receiver which reduces the number of operations required to change the operating mode of the scanner while at the same time providing a more direct approach for selecting a subgroup of one or more preselected broadcast channels and/or bypassing one or more preselected broadcast channels.